D.c. to d.c. voltage converter with undervoltage-responsive, mode selector means



March 21, 1967 J. B. FLANNERY I 3,310,727

D.C. T0 D.G. VOLTAGE CONVERTER WITH UNDERVOL'IAGE-RESPONSIVE, MODESELECTOR MEANS Filed Sept. 26, 1963 55 "I I I I I 34 l I I OL/fP/f 3 #6I I I ma I wPuf/MK) I 705- I I I 65 I I I I I I I I I L J I NVEN TOR.(fay/v.5. fZ/l/V/VEFX United States Patent ice D.C. T0 D.C. VOLTAGECONVERTER WITH UNDERVGLTAGE-RESPONSIVE, MODE SE- LECTOR MEANS John B.Flannery, Chelmsford, Mass, assignor to Ovitron Corporation, Newburgh,N.Y., a corporation of Delaware Filed Sept. 26, 1963,. Ser. No. 311,8445 Claims. (Cl. 321-14) This invention relates to a voltage converter andmore particularly to a converter which utilizes transistors to convert aDC potential from one level to another.

Diesel locomotives have come into wide use in recent years. In order tostart these locomotive engines, a DC. battery source is employed and forvarious important design reasons relating the starting equipment, abattery voltage of 74 volts has been Widely used. However, certain tracksafety equipment has for some time been standardized for operation at 32volts DC. and it is therefore necessary to convert from the .D.C.voltage of 74 volts to a DC. voltage of 32 volts. In the prior art thishas been accomplished by a motor-generator set. The motor-generator set,however, is relatively expensive and must be reconditioned or rebuiltabout once a year at a substantial cost to from 30 to 40% of theoriginal cost of the unit.

Accordingly, it is an object of this invention to make availableapparatues for converting a DC. potential from one value to anotherwhich is less expensive than an equivalent motor-generator set forproducing the same output power. I

It is another object of the invention to provide apparatus forconverting a DC. voltage of given value to a value approximately half ofthat value.

A further object of the invention is to eliminate the high maintenancecost required by motor-generator sets presently employed on moderndiesel locomotives.

One of the features of the invention lies in the provision of a modeselector for providing a voltage at a pair of output terminals byautomatically connecting the terminals either directly to the inputvoltage when it is at a predetermined reduced value or to the reducedoutput voltage of the converter circuit.

Another feature of the invention lies in the provision of voltageregulator means for maintaining the voltage output of the regulatorwithin predetermined limits.

All of the objects, features and advantages of this invention and themanner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawing which shows a schematic diagram of a convertercircuit in accordance with the invention.

In the drawing, which shows an arrangement particularly suitable for usewith diesel locomotives, there is provided a pair of input terminals aand 10b for receiving an input voltage of 74 volts, and a pair of outputterminals 11a and 11b for providing an output voltage normally having avalue of approximately 32 volts. A transformer 12 is employed to aid inproviding the volt-age conversion, this transformer having three similarprimary windings 13, 13' and 13", and a secondary winding 14. Each ofthe transformer primary windings 13, 13' and 13" forms part of a more orless independent circuit, indicated as bank 1, bank 2 and bank 3, eachbank being shown separately within a dashed line rectangle.

In bank 1 there is provided two transistors 17 and 18 which may beeither NPN or PNP type, PNP type being shown in the drawing. Thecollector electrodes 22 and 25, respectively, of these transistors 17and 18 are con-' 3,310,727 Patented Mar. 21, 1967 nected to a wire 26for receiving a collector operating potential which is more negativethan the positive potential on the input terminal 1%. The emitters 20and 23 of the transistors 17 and 18 are connected, respectively, to theterminals 13b and 13d of the transformer primary winding 13. The portionof the winding 13 between the terminals 13b and 13d is center tapped atthe terminal 13c, this latter terminal being connected to the positiveinput terminal 10b. The base electrodes 21 and 24 of the transistors 17and 18 are connected, respectively, to the primary terminals 13a and 13ethrough biasing resistors 27 and 28. The portion of the winding 13between the terminals 13a and 13b and the portion between the terminals13d and 13e comprise biasing windings for the transistors to which theyare connected. The transistor 17 in bank 1 is the starting transistor,as between two transistors 17 and 18, and is therefore provided with astarting resistor 29 connected between the base and coilector electrodes21 and 22.

The circuitry and components in each of the banks 2 and 3 are identicalto that of bank 1. These additional banks are provided to increase thepower output to three times that which can be provided by only one bank.In banks 2 and 3, like components as those in bank 1 are designated,respectively, with a prime and double prime designation following thenumeral.

The circuits of each of the banks also include a circuit to protect thetransistors therein against damage due to transient voltages, such asspike potentials which are developed in the voltage input circuit atvarious times during operation of the diesel engine. These protectioncircuits include Zener diodes 30, 30' and 30" which are connectedbetween the positive and negative potential supply points for theparticular bank; thus, for bank 1 the diode is connected between thewire 26 and the positive input terminal 10b. Each diode 30, 30 and 30'has a breakdown potential sufficient to cause conduction at apredetermined level, so that no transient potential above this level canreach the transistors in the different banks to cause damage thereto.breakdown level will depend to some extent upon the particulartransistors employed. The diodes 30, 30 and 30" are preferably, thoughnot necessarily bridged by resistors 31, 31' and 31", each having avalue, such as for example, 10,000 ohms.

Resistors 34 and 35, through which operating potential is supplied tothe various banks from the negative input terminal 10a, also comprise apart of the transistor protection circuit. The over-all resistance ofthese resistors 34 and 35 is chosen to match the dynamic impedance ofthe Zener diodes 30, 30 and 30". These diodes and the resistors 34 and35 cooperate with one another to provide full protection for thetransistors in the three banks against the transient voltages referredto above.

, The circuits within each of the banks 1, 2 and 3 function much in thesame manner as a flip-flop circuit, well known in the art. Consideringonly bank 1 for purposes of explanation, when operating potential isapplied thereto, the transistor 17 is caused to conduct, however, thistransistor soon becomes saturated, causing it to become non-conductiveand the transistor 18 to become conductive. The transistor 18 in likemanner then becomes saturated causing it to become non-conductive, atwhich time the transistor 17 again becomes conductive. This processcontinues so long as operating potential is applied. Due to this on-offswitching action of the transistors 17 and 18, a pulsating DC currentpasses through the primary winding 13 causing an AC. potential to bedeveloped in the secondary winding 14. The banks 2 and 3 'function inthe same manner and simultaneously with bank 1 to increase the poweravailable from the winding 14.

This particular predetermined The A.C. developed in the secondarywinding 14 is rectified by a conventional full wave rectifier circuit36, providing a DC. voltage at the output terminals 37a and 37b thereof.The rectifier output terminal 37 b is connected to the positiveconverter output terminal 11b through a wire 38, a contact 39 andarmature 49 of a relay 41, and a wire 42. The rectifier output terminal37a is connected to the negative converter output terminal 11a through awire 43 into a voltage regulator 44, out of the voltage regulator viawire 45, through a contact 46 and arm 47 of the relay 41, and a wire 43.

The voltage regulator 44 includes a pair of transistors 49 and 50 of thePNP type connected in parallel with one another. These two transistorsare connected in series between the rectifier output terminal 37a andthe negative converter output terminal 11a when the relay arm 47 is inelectrical contact with the contact point 46. These two transistors 49and 50 are controlled by a PNP type transistor 51 and an NPN typetransistor 52 cooperating therewith. The emitter 53 of the transistor 51is connected to the arm of an adjustable resistor 59 which may be variedto set the voltage level at the converter output terminals 11a and 11b.This adjustable resistor 59 is connected between the output terminals11a and 11b when the relay 41 is in the energized position shown in thedrawing, and functions as a voltage change sensing resistor in thevoltage regulator 44, as will be seen. The base 54 of the transistor 51is connected to the junction point between a resistor 60 and a Zenerdiode 61, these being connected in series between the rectifier outputterminals 37a and 37b. The collector 55 of the transistor 51 isconnected to a collector load resistor 62. This load resistor 62 isconnected in series with a resistor 63, the latter being-connectedbetween the emitter 56 and base 57 of the transistor 52. The resistors62 and 63 are connected in series with a resistor 64 to the negativerectifier output terminal 37a. The collector 58 of the transistor 52 isconnected to a collector load resistor 65; it is also connected to thebase electrodes 66 and 67 of the transistors 49 and 50 through resistors68 and 69, respectively.

When a change tends to occur in the value of the voltage at theconverter output terminals 11a and 115, the voltage at the arm of theadjustable resistor 59 will also change, since this resistor isconnected across these terminals, causing the bias on the transistor 51to change. This in turn causes a change in the conduction of thetransistor 51, resulting in a change in the voltage drop across theresistors 62 and 63. This in turn changes the bias on the transistor 52,altering its conduction and thus also the value of the IR drop acrossthe collector load resistor 65. This IR drop change is reflected in achange of the bias on the base electrodes 66 and 67 of the transistors49 and 50, respectively, producing a change in conduction in thesetransistors. The direction of this change is such as to oppose thechange in the voltage at the output terminals 11a and 11b which causedit. Thus, when the voltage across the output terminals 11a and 11];tends to either increase or decrease, the circuit of the voltageregulator 44, which is essentially a negative feedback loop, willmaintain this output voltage at a constant level of approximately 32volts.

As noted above, the converter circuit of this invention is designedespecially for use with diesel locomotives, and during normal operationthe voltage regulator 44 will maintain the output voltage atapproximately 32 volts. However, when the diesel must be started, eitherinitially or after stalling, the input voltage at the terminals a and10b drops from a value of 74 volts to approximately 35 volts. Thiscauses the output voltage at the terminals 11a and 11b to drop to avalue of about volts, which is insufficient to operate the safetyequipment to which it must supply power. This invention, therefore,includes a mode selector for automatically disconnecting the voltageregulator 44 during the period when the diesel is being started andconnecting the output terminals 11a and 11b directly to the inputtreminals 10a and ltlb. This mode selector comprises the relay 41 inwhich the coil 71 is connected in series with a Zener diode 72 acrossthe input terminals 10a and 10b. This Zener diode is selected to have acharacteristic such that it is conductive only at values slightlygreater than the 35 volt value to which the input potential of 74 voltswill drop when the diesel is being started. At this lower value of 35volts therefore, the relay will drop open so that the armatures 40 and47 are in the position shown by the dashed lines, in contact withcontact points 73 and '75. In this unenergized position the outputterminals 11a and 11b are directly connected through the contacts 73 andto the input terminals 10a and 10b. Thus, the voltage of 35 volts, avalue less than 10% over the desired value of 32 volts, will beavailable to operate the track safety equipment during starting of thediesel engine. When the diesel has been started the heavy load on thestarting battery no longer exists and the input voltage therefore willreturn to a value of 74 volts. The Zener diode 72 will therefore becomeconductive, energizing the relay 41 to connect the output terminals 11aand 11b to the output of the con verter through the relay contacts 39and 46.

The utilization of the device described herein allows significantsavings both in terms of initial cost and main tenance. Morespecifically, the motor-generator sets of type referred to above costapproximately $450. The apparatus described according to the inventionherein provides the electrical output necessary to operate the tracksafety equipment at a cost of only 45 to 55% of the cost of themotor-generator. Additionally, the motorgenerator set requires majoroverhauls approximately every year and this costs approximately 30 to40% of the cost of a new motor-generator set. By sharp contrast theconverter system described herein requires no such periodic overhaul andmay operate for years without causing even minor technical difficulties.Furthermore, the converter device has an indefinite life, which is nottrue of the motor-generator set, since the bearings and commutators aresubject to continuous wear.

While the foregoing description sets forth the principles of theinvention in connection with specific apparatus, it is to be understoodthat the description is made only by way of example and not as alimitation of the scope of the invention as set forth in the objectsthereof and in the accompanying claims.

What is claimed is:

1; A power supply conversion system comprising a pair of input terminalsfor receiving a DC. input potential having a given value,

a transformer,

a semiconductor switching circuit including a plurality of transistorsconnected to said input treminals for delivering a pulsating current tothe primary Winding of said transformer, whereby an A.C. potential isinduced in the secondary winding of said transformer,

means connected to said transformer secondary for rectifying said A.C.potential,

voltage regulator means connected to said rectifier means formaintaining the level of said rectified potential Within predeterminedlimits,

a pair of output terminals,

and mode selector means connected to said output terminals, to saidregulator means and to said input terminals, said mode selector meansbeing operable to connect said output terminals to the output from saidregulator when said input potential is at approximately said givenvalue, and to connect said output terminals directly to said inputterminals when the input potential drops to a predetermined value belowsaid given value.

2. The invention described in claim 1 wherein said mode selector meansincludes an electromagnetically actuated switch and a diode, said diodebeing connected in series with the coil of said switch across said inputterminals, said diode further being non-conductive below said potentialof given value and conductive above said potential of given value.

3. The invention described in claim 1 which further includes voltageprotection means connected to said transistors to protect saidtransistors from the damaging effects of transient spike potentialsabove a predetermined value originating in the circuit connected to saidinput terminals, said voltage protection means including a diodeconnected in series with means for matching the dynamic impedance ofsaid diode.

4. A power supply conversion system comprising a pair of input terminalsfor receiving a DC. input potential having a given value,

a circuit responsive to transient spike potentials connected betweensaid input terminals, said circuit including a Zener diode in serieswith a. resistor for matching the dynamic impedance of said diode,

a transformer,

a semiconductor switching circuit including a plurality of transistorsconnected across said diode for delivering a pulsating current to theprimary winding of said transformer, whereby an AC. potential is inducedin the secondary winding of said transformer,

means connected to said transformer secondary for rectifying said A.C.potential,

voltage regulator means connected to said rectifier means formaintaining the level of said rectified potential within predeterminedlimits,

a pair of output terminals,

and mode selector means connected to said output terminals, to saidregulator means and to said input termnials, said mode selector meansbeing operable to connect said output terminals to the output from saidregulator when said input potential is at approximately said givenvalue, and to connect said output terminals directly to said inputterminals when the input potential drops to a predetermined value belowsaid given value.

5. A power supply conversion system comprising a pair of input terminalfor receiving a D.C. input potential having a given value,

a transformer,

a semiconductor switching circuit including a plurality of transistorsconnected to said input terminals for delivering a pulsating current tothe primary winding of said transformer, whereby an AC. potential isinduced in the secondary winding of said transformer,

voltage protection means connected to said input terminals and to saidtransistors to protect said transistors from the damaging effects oftransient spike potentials above a predetermined value, said voltageprotection means including a diode in series with means for matching thedynamic impedance of said diode,

means connected to said transformer secondary for rectifying said A.C.potential,

voltage regulator means connected to said rectifier means formaintaining the level of said rectified potential within predeterminedlimits,

a pair of output terminals,

and mode selector means, said mode selector means including a currentactuated switch having a coil connected in series with a diode acrosssaid input terminals, said switch being connected to said outputterminals, to said regulator means and to said input terminals, saidmode selector means being operable to connect said output terminals tothe output from said regulator when said input potential is atapproximately said given value, and to connect said output terminalsdirectly to said input terminals when the input potential drops to apredetermined value below said given value.

References Cited by the Examiner UNITED STATES PATENTS 1/1966 Gilbert eta1 321-11 JOHN F. COUCH, Primary Examiner.

W. H. BEHA, Assistant Examiner.

1. A POWER SUPPLY CONVERSION SYSTEM COMPRISING A PAIR OF INPUT TERMINALSFOR RECEIVING A D.C. INPUT POTENTIAL HAVING A GIVEN VALUE, ATRANSFORMER, A SEMICONDUCTOR SWITCHING CIRCUIT INCLUDING A PLURALITY OFTRANSISTORS CONNECTED TO SAID INPUT TERMINALS FOR DELIVERING A PULSATINGCURRENT TO THE PRIMARY WINDING OF SAID TRANSFORMER, WHEREBY AN A.C.POTENTIAL IS INDUCED IN THE SECONDARY WINDING OF SAID TRANSFORMER, MEANSCONNECTED TO SAID TRANSFORMER SECONDARY FOR RECTIFYING SAID A.C.POTENTIAL, VOLTAGE REGULATOR MEANS CONNECTED TO SAID RECTIFIER MEANS FORMAINTAINING THE LEVEL OF SAID RECTIFIED POTENTIAL WITHIN PREDETERMINEDLIMITS, A PAIR OF OUTPUT TERMINALS,